objectives: Subarachnoid hemorrhage (SAH) is a subtype of stroke, and early brain injury (EBI) is a contributor to its unfavorable outcome. microRNA (miRNA) is abundantly expressed in the brain and participates in brain injury. This study investigated the effect of miR-452-3p on EBI after SAH. methods: The murine model of SAH was established. miR-452-3p expression was detected 48 h after the model establishment. Neurobehavioral function, blood-brain barrier permeability, brain water content, neuronal apoptosis, and inflammatory factors were evaluated. The cell model of SAH was induced by oxygen hemoglobin. Apoptosis rate, lactate dehydrogenase, and reactive oxygen species were detected. The targeting relationship between miR-452-3p and histone deacetylase 3 (HDAC3) was verified. The acetylation of p65 and the binding of HDAC3 to p65 were detected. The inhibitory protein of the nuclear factor κB pathway (IκBα) was detected. Suberoylanilide hydroxamic acid was injected into the SAH mice treated with miR-452-3p inhibitor. results: SAH mice showed upregulated miR-452-3p expression; reduced the neurological score; increased blood-brain barrier permeability, brain water content, and neuronal apoptosis; elevated pro-inflammatory factors; and reduced anti-inflammatory factors. SAH increased the apoptosis rate, lactate dehydrogenase release, and reactive oxygen species levels in oxygen-hemoglobin-treated neuron cells. Inhibition of miR-452-3p reversed the above trends. miR-452-3p targeted HDAC3. SAH upregulated p65 acetylation. miR-452-3p inhibitor promoted the binding of HDAC3 to p65, decreased p65 acetylation, and upregulated IκBα. Suberoylanilide hydroxamic acid reversed the protective effect of miR-452-3p inhibitor on SAH mice and aggravated brain injury. conclusions: miR-452-3p targeted HDAC3 to inhibit the deacetylation of p65 and activate the nuclear factor κB pathway, thus aggravating EBI after SAH.